The present invention relates to thermoplastic compositions based on grafted rubber and polyester, a process for their manufacture, and industrial articles obtained from the compositions.
Examples in published European Patent Application No. 0,056,123 describe the preparation of a thermoplastic mass comprising 90% by weight of polybutylene terephthalate (PBTP) and 10% by weight of a grafted rubber, by mixing in an extruder at 250.degree. C. the PBTP and a grafted rubber produced in an aqueous dispersion and containing 35% by weight of water.
A slightly modified impact-polystyrene comprising:
from 20 to 80% by weight of a vinylaromatic polymer modified by the presence of 5 to 15% by weight of an unsaturated nitrile and, where applicable, a rubber, and PA1 from 20 to 80% by weight of a crystalline polyester having a molecular weight of preferably 10,000 to 60,000 PA1 the crystalline polyester is polybutylene terephthalate, and PA1 the polymer based on a vinylaromatic monomer, nitrile, and rubber is a specific polymer according to the present invention, different from the polymers used in the prior art.
is known from British Patent No. 2,118,194.
More precisely, Example 6 of this document describes a mixture of 75% by weight of a modified polystyrene (consisting of 84% by weight of styrene, 8% by weight of acrylonitrile and 8% by weight of rubber) and of 25% by weight of polybutylene terephthalate. This mixture has an Izod impact resistance of 49 J/m, considerably lower than that of the initial modified polystyrene.
Furthermore, French Patent No. 2,154,800, and especially its Example 20, discloses a mixture of 20% by weight of high molecular weight polybutylene terephthalate, 60% by weight of a terpolymer of acrylonitrile, butadiene and styrene, and 20% by weight of glass fiber reinforcement. This mixture has an Izod impact resistance of 65 J/m, well below that of a similar binary mixture in which the polybutylene terephthalate is replaced by the terpolymer of acrylonitrile, butadiene, and styrene.
Thus, according to the teaching of the prior art, the introduction of 20 to 25% by weight of a high molecular weight crystalline polyester into a polymer based on styrene, acrylonitrile, and rubber results in a decrease in the impact strength of the composition, whether the latter is filled or not.